Is the word "has" a helping verb in the question: "What has John promised you?".
It doesn't seem to have any meaning of possession.
What has John promised you? "Has" is the present tense of the perfect auxiliary "have", which in combination with the past participle "promised" forms the perfect tense. Many people do call such auxiliaries "helping verbs".
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What has John promised you?
"Has" is the present tense of the perfect auxiliary "have", which in combination with the past participle "promised" forms the perfect tense.
Many people do call such auxiliaries "helping verbs".
"What has John promised you?"
You could answer eg "He has promised me a bicycle". Perhaps you can see more easily here that it is the Present Perfect tense.